I’m using Quest 2 with Oculus Link to do VR previews in both 4.25 and 4.26.1 without the performance problem you describe. I’m not sure what may be different in your project/system, but here are some things to check.
Go to Editor Preferences > General - Performance > Editor Performance and disable “Use Less CPU when in Background” if you haven’t already. If you don’t disable this then if any other app on your system comes to the foreground while previewing your VR scene you will definitely see significantly low frame rates.
Another thing is to reference Oculus’s own Unreal Engine: Oculus Quest Quick Start for their recommended project settings and make sure you’re using them for your project.
FWIW, I have my project configured to use Forward Rendering. I believe on Quest (and all Android devices) Forward Rendering will be used regardless of what you have this option set to, but with it enabled you will be assured that the Forward Renderer is used during in-editor previews as well when running on device.